1. Field
The present invention relates to an electrolyte for rechargeable lithium battery and a rechargeable lithium battery including the same.
2. Description of the Related Art
Energy storage technologies have recently been drawing attention. As the application of energy storage technologies is widened into the fields of mobile phones, camcorders, laptop computers, personal computers (PCs), and even automobiles, the demand for high energy densification of a battery that is used as power source of for electronic devices is increasing.
A rechargeable lithium battery is a battery that best satisfies the high energy demand of these technologies, and researchers are studying rechargeable lithium batteries in more detail. A rechargeable lithium battery includes a positive electrode including a positive active material that intercalates and deintercalates lithium, a negative electrode including a negative active material that intercalates and deintercalates lithium, and an electrolyte.
When a rechargeable lithium battery is initially charged, the lithium ions that come out of the positive active material, such as lithium transition metal oxide, transfer to the negative active material and are implanted between the layers of the negative active material. Because lithium has strong reactivity, the electrolyte and a lithium salt react with each other on the surface of the negative active material to form a solid electrolyte interface (SEI) film.
The SEI film serves as an ion tunnel and allows only lithium ions to pass through. The SEI film prevents organic solvent molecules having a high molecular weight from transferring along with the lithium ions in the electrolyte, thereby preventing the high molecular weight organic solvent molecules from being implanted between the layers of the negative active material and destroying or damaging the structure of the negative electrode. Therefore, as the SEI film prevents contact between the organic solvent molecules in the electrolyte and the negative active material, the electrolyte does not decompose and the amount of lithium ions in the electrolyte solution is maintained. Thus, stable charge and discharge characteristics may be obtained.
The formation of the stable SEI film is related to the charge and discharge rate capability and cycle-life of the rechargeable lithium battery. Particularly, since a hybrid battery, such as an ISG (Idle Stop and Go) battery for automobiles, concurrently (e.g., simultaneously) requires a high charge and discharge rate capability, stable cycle-life characteristics, and stability at a low temperature, it is more important to form a stable SEI film.